feat: Implements passive Detect Hidden mechanics (#2342)

Projects/Server.Tests/Helpers/PredictableRandom.cs

@@ -0,0 +1,43 @@
+using System;
+using Server.Random;
+
+namespace Server.Tests;
+
+/// <summary>
+/// Replaces <see cref="BuiltInRng.Generator"/> with a <see cref="System.Random"/> that returns
+/// a fixed value, making skill checks and other RNG-dependent code deterministic in tests.
+/// Restores the original generator on <see cref="Dispose"/>.
+/// <para>Usage:</para>
+/// <code>
+/// using var rng = new PredictableRandom(10); // Utility.Random(21) returns 10
+/// </code>
+/// </summary>
+public sealed class PredictableRandom : IDisposable
+{
+    private readonly System.Random _original;
+
+    public PredictableRandom(int fixedValue)
+    {
+        _original = BuiltInRng.Generator;
+        BuiltInRng.Generator = new FixedRandom(fixedValue);
+    }
+
+    public void Dispose()
+    {
+        BuiltInRng.Generator = _original;
+    }
+
+    private sealed class FixedRandom(int value) : System.Random
+    {
+        public override int Next() => value;
+        public override int Next(int maxValue) => Math.Clamp(value, 0, maxValue - 1);
+        public override int Next(int minValue, int maxValue) => Math.Clamp(value + minValue, minValue, maxValue - 1);
+        public override long NextInt64() => value;
+        public override long NextInt64(long maxValue) => Math.Clamp(value, 0, maxValue - 1);
+        public override long NextInt64(long minValue, long maxValue) => Math.Clamp(value + minValue, minValue, maxValue - 1);
+        public override double NextDouble() => Math.Clamp(value / 20.0, 0.0, 1.0);
+
+        public override void NextBytes(byte[] buffer) => Array.Fill(buffer, (byte)Math.Clamp(value, 0, 255));
+        public override void NextBytes(Span<byte> buffer) => buffer.Fill((byte)Math.Clamp(value, 0, 255));
+    }
+}